A lithium secondary cell includes a positive electrode that includes a positive electrode current collector (e.g. an aluminum foil) and a positive electrode mixture layer containing a positive electrode active material (e.g. a lithium-containing complex oxide) on the positive electrode current collector; a negative electrode that includes a negative electrode current collector (e.g. an aluminum foil) and a negative electrode mixture layer containing a negative electrode active material (e.g. a carbonous material) on the negative electrode current collector; and a nonaqueous electrolytic solution containing an electrolyte salt (e.g. a lithium salt) and an organic solvent.
One disadvantage of this lithium secondary cell structure is that the electrolyte salt (e.g. a lithium salt) in the electrolytic solution anodizes the current collector, and therefore causes corrosion thereof, and in turn, causes the cycle characteristic and capacity of the cell to deteriorate.
Some attempts have been made to prevent or delay the above-described mechanism of current collector corrosion. Described in Patent Literature 1 is formation of a surface protective layer containing a heterocyclic compound on a current collector. Additionally, Patent Literature 2 discloses formation of a protective layer containing at least one selected from noble metals, alloys, conductive ceramics, semiconductors, organic semiconductors, and conductive polymers, on a positive electrode current collector (an aluminum foil) to prevent the current collector from corroding due to a lithium imide salt that is present as an electrolyte salt, and specifically teaches, as conductive polymers, polyaniline, polypyrrole, polyacene, polydisulfide, and polyparaphenylene. One exemplary method for forming a protective layer using a conductive polymer described therein is a method involving casting or coating a mixture solution containing a conductive polymer, a binder, and a dopant (an aromatic sulfonic acid ester) dissolved in a solvent, and heating and drying the coat.
In addition, Patent Literature 3 describes formation of a conductive adhesive layer by spraying a slurry containing carbon black to a current collector (see [0039]).
Patent Literature 4 describes use of an epoxy resin as a binder in a paste for forming current collector protective layers.